Comparison of the effects of an intravenous lidocaine infusion combined with 1% isoflurane versus 2% isoflurane alone on selected cardiovascular variables and recovery characteristics during equine general anaesthesia.

This study compares the effects of combining lidocaine infusion with 1% isoflurane versus 2% isoflurane alone on cardiovascular variables in anaesthetized horses. The findings suggest that lidocaine with 1% isoflurane might improve cardiovascular variables, but a large sample size would be necessary to detect any significant difference in the recovery quality.

Research Design

• This is a prospective, randomized, blinded, crossover study which involves twelve healthy horses as experimental subjects.
• The horses were anaesthetized twice using several specific intravenous (IV) medications and then placed in dorsal recumbency and ventilated mechanically.
• During the initial phase of anesthesia (P1), all horses were maintained on a 2% inspired isoflurane fraction (FIIso). In the next phase of anesthesia (P2), horses either received an IV lidocaine or saline. In the final phase of anesthesia (P3), one group received a constant rate infusion (CRI) of lidocaine along with 1% FIIso, and the other group received a saline CRI and 2% FIIso. Three weeks later, the horses received the other treatment, hence the crossover design.

Procedure

• Painful stimuli were caused to the horses by introducing an 18 gauge needle intramuscularly. This likely simulated a surgical procedure or induced stress to better understand the effectiveness of the anesthesia.
• Various requirements, such as need for supplementary anesthetics like ketamine and dobutamine, and physiological variables were recorded.
• Additionally, recoveries of the horses were assessed by two anaesthetists who were not aware of the treatment group of the horses, maintaining blindness in the experiment.
• Finally, the lidocaine plasma concentrations were measured during the recovery stage.

Results

• During the last phase of anesthesia (P3), the horse group receiving lidocaine CRI and 1% FIIso showed a lower heart rate, higher mean arterial pressure and required less dobutamine compared to the group receiving saline and 2% FIIso.
• However, in one horse, lidocaine plasma concentrations reached toxic levels. On the other hand, recovery rates did not significantly vary between the two groups.
• The researchers estimated that a sample size of 208 horses per group would be necessary to determine a significant difference in recovery quality with an 85% statistical power. This suggests that the sample size of 12 horses in the study may have been too small to detect small effect sizes.

Conclusion

• The research concluded that a lidocaine CRI combined with FIIso 1% may improve cardiovascular variables in healthy anesthetized horses compared to using FIIso 2% alone.
• However, to ascertain the effect on the recovery quality, larger sample sizes will be necessary in future studies.